Development in the optical recording which utilizes laser technology has been desired particularly in recent years owing to its capability of preservation and reproduction of information recorded in high density.
As one example of such optical recording, there may be mentioned an optical disc.
In general, the optical disc carries out high density recording of information by irradiation of laser beam which has been collimated to a beam diameter of 1 .mu.m or so onto a thin recording layer provided on a circular base member
The information recording is effected by thermal deformation of the recording layer such as its decomposition, evaporation, dissolution, and others which take place at particular portions of the recording layer owing to its absorption of the laser energy as irradiated onto it. On the other hand, the reproduction of the recorded information is done by reading of a difference in the reflection factor between the portion where the deformation has taken place by the laser beam and the portion where no deformation has occurred.
For the recording member, therefore, it is necessary to have high absorptivity to the laser beam of a particular wavelength to be used for the recording, because the recording member is required to absorb energy of the laser beam with good efficiency, and also to have high reflection factor to the laser beam of a particular wavelength for use in the reproduction so as to carry out the accurate reproduction of the recorded information.
For such optical recording member, there have so far been proposed various inorganic compounds such as metals, metal compounds, chalcogenides, and so on. However, the thin films made of these inorganic compounds have various disadvantages such that they are susceptible to oxidation in the air, difficult to preserve over a long period of time, sensitive to the ultraviolet part or the visible part of the light rays, not durable against sun light and other light, and so forth.
As the organic compounds to be used for the recording member, there have so far been proposed cyanine type coloring matter, squalerium type coloring matter, naphthoquinone type coloring matter, phthalocyanine type coloring matter, and so on. Of these various coloring matters, the phthalocyanine type coloring matter is highly stable to the ultraviolet part and the visible part of the light rays, while it is remarkably inferior in its solubility to organic solvents, hence it has a shortcoming such that the economically advantageous coating method cannot be adopted for the thin film forming.